diff options
author | Manfred Spraul <manfred@colorfullife.com> | 2018-08-22 07:01:25 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-08-22 19:52:51 +0200 |
commit | e2652ae6bd7492cdc0436817cbcd09282eb0bb03 (patch) | |
tree | 3736e02fc0a194548e10bf40680b22d737f6b320 /ipc/util.c | |
parent | ipc: compute kern_ipc_perm.id under the ipc lock (diff) | |
download | linux-e2652ae6bd7492cdc0436817cbcd09282eb0bb03.tar.xz linux-e2652ae6bd7492cdc0436817cbcd09282eb0bb03.zip |
ipc: reorganize initialization of kern_ipc_perm.seq
ipc_addid() initializes kern_ipc_perm.seq after having called idr_alloc()
(within ipc_idr_alloc()).
Thus a parallel semop() or msgrcv() that uses ipc_obtain_object_check()
may see an uninitialized value.
The patch moves the initialization of kern_ipc_perm.seq before the calls
of idr_alloc().
Notes:
1) This patch has a user space visible side effect:
If /proc/sys/kernel/*_next_id is used (i.e.: checkpoint/restore) and
if semget()/msgget()/shmget() fails in the final step of adding the id
to the rhash tree, then .._next_id is cleared. Before the patch, is
remained unmodified.
There is no change of the behavior after a successful ..get() call: It
always clears .._next_id, there is no impact to non checkpoint/restore
code as that code does not use .._next_id.
2) The patch correctly documents that after a call to ipc_idr_alloc(),
the full tear-down sequence must be used. The callers of ipc_addid()
do not fullfill that, i.e. more bugfixes are required.
The patch is a squash of a patch from Dmitry and my own changes.
Link: http://lkml.kernel.org/r/20180712185241.4017-3-manfred@colorfullife.com
Reported-by: syzbot+2827ef6b3385deb07eaf@syzkaller.appspotmail.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to '')
-rw-r--r-- | ipc/util.c | 91 |
1 files changed, 48 insertions, 43 deletions
diff --git a/ipc/util.c b/ipc/util.c index fdffff41f65b..e5c9e2b2e4c4 100644 --- a/ipc/util.c +++ b/ipc/util.c @@ -194,46 +194,54 @@ static struct kern_ipc_perm *ipc_findkey(struct ipc_ids *ids, key_t key) return NULL; } -#ifdef CONFIG_CHECKPOINT_RESTORE /* - * Specify desired id for next allocated IPC object. + * Insert new IPC object into idr tree, and set sequence number and id + * in the correct order. + * Especially: + * - the sequence number must be set before inserting the object into the idr, + * because the sequence number is accessed without a lock. + * - the id can/must be set after inserting the object into the idr. + * All accesses must be done after getting kern_ipc_perm.lock. + * + * The caller must own kern_ipc_perm.lock.of the new object. + * On error, the function returns a (negative) error code. */ -#define ipc_idr_alloc(ids, new) \ - idr_alloc(&(ids)->ipcs_idr, (new), \ - (ids)->next_id < 0 ? 0 : ipcid_to_idx((ids)->next_id),\ - 0, GFP_NOWAIT) - -static inline int ipc_buildid(int id, struct ipc_ids *ids, - struct kern_ipc_perm *new) +static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new) { - if (ids->next_id < 0) { /* default, behave as !CHECKPOINT_RESTORE */ + int idx, next_id = -1; + +#ifdef CONFIG_CHECKPOINT_RESTORE + next_id = ids->next_id; + ids->next_id = -1; +#endif + + /* + * As soon as a new object is inserted into the idr, + * ipc_obtain_object_idr() or ipc_obtain_object_check() can find it, + * and the lockless preparations for ipc operations can start. + * This means especially: permission checks, audit calls, allocation + * of undo structures, ... + * + * Thus the object must be fully initialized, and if something fails, + * then the full tear-down sequence must be followed. + * (i.e.: set new->deleted, reduce refcount, call_rcu()) + */ + + if (next_id < 0) { /* !CHECKPOINT_RESTORE or next_id is unset */ new->seq = ids->seq++; if (ids->seq > IPCID_SEQ_MAX) ids->seq = 0; + idx = idr_alloc(&ids->ipcs_idr, new, 0, 0, GFP_NOWAIT); } else { - new->seq = ipcid_to_seqx(ids->next_id); - ids->next_id = -1; + new->seq = ipcid_to_seqx(next_id); + idx = idr_alloc(&ids->ipcs_idr, new, ipcid_to_idx(next_id), + 0, GFP_NOWAIT); } - - return SEQ_MULTIPLIER * new->seq + id; + if (idx >= 0) + new->id = SEQ_MULTIPLIER * new->seq + idx; + return idx; } -#else -#define ipc_idr_alloc(ids, new) \ - idr_alloc(&(ids)->ipcs_idr, (new), 0, 0, GFP_NOWAIT) - -static inline int ipc_buildid(int id, struct ipc_ids *ids, - struct kern_ipc_perm *new) -{ - new->seq = ids->seq++; - if (ids->seq > IPCID_SEQ_MAX) - ids->seq = 0; - - return SEQ_MULTIPLIER * new->seq + id; -} - -#endif /* CONFIG_CHECKPOINT_RESTORE */ - /** * ipc_addid - add an ipc identifier * @ids: ipc identifier set @@ -251,7 +259,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) { kuid_t euid; kgid_t egid; - int id, err; + int idx, err; if (limit > IPCMNI) limit = IPCMNI; @@ -271,30 +279,27 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit) new->cuid = new->uid = euid; new->gid = new->cgid = egid; - id = ipc_idr_alloc(ids, new); + idx = ipc_idr_alloc(ids, new); idr_preload_end(); - if (id >= 0 && new->key != IPC_PRIVATE) { + if (idx >= 0 && new->key != IPC_PRIVATE) { err = rhashtable_insert_fast(&ids->key_ht, &new->khtnode, ipc_kht_params); if (err < 0) { - idr_remove(&ids->ipcs_idr, id); - id = err; + idr_remove(&ids->ipcs_idr, idx); + idx = err; } } - if (id < 0) { + if (idx < 0) { spin_unlock(&new->lock); rcu_read_unlock(); - return id; + return idx; } ids->in_use++; - if (id > ids->max_id) - ids->max_id = id; - - new->id = ipc_buildid(id, ids, new); - - return id; + if (idx > ids->max_id) + ids->max_id = idx; + return idx; } /** |